Extensively tested and found following settings to work reliably:
Device Type = 5 Ericsson
Serial Port = COM8 (port of the device called Sony Ericsson PC300 Mobile Broadband Command Interface)
Connection modes automatic and dial-up do work, network using the WDM and NDIS devices does not work so far.
It works with the drivers contained in the original wireless manager 5.0.0.135 package, no need to install the full wireless manager application.